This invention relates to a selective reduction type, high temperature superconductor, which is a copper (Cu) oxide, high temperature superconductor that permits doping with positive holes by selectively reducing constituent elements (atoms). This superconductor can be used in large scale superconducting power transmission, superconducting power storage or reserve, superconducting electronics such as a high performance Josephson device, a high frequency device or the like. The invention also relates to methods of making such a superconductor.
Conventional Cu-oxide family, high temperature superconductors have been prepared doping with positive holes, by oxidation, to raise the contents of the superconducting carriers. Such a high temperature superconductor, however, may cause the carriers to reduce in concentration due to diffusion or bleeding of oxygen atoms by increased temperature. This leads to a depletion in superconductivity of the superconductor.
Also, doping with positive holes to obtain a higher carrier concentration has been thought to require a higher oxygen partial pressure, and it has so far been unattainable to prepare a superconductor of the type described by doping with positive holes to raise the carrier concentration in a reduction process conditioned under low partial pressure or vacuum. Since it has been found impossible to increase the concentration of positive holes by reduction, i.e., by lowering the oxygen partial pressure, the conventional high temperature superconductors have the problem that they have a limited carrier concentration and are thus low and unsatisfactory in their superconducting properties that include the critical temperature Tc, critical current density Jc, irreversible magnetic filed Hirr. It has therefore been sought to, solve the problem of bringing into realization a high temperature superconductor of a reduced oxygen concentration.
With these problems taken into account, it is accordingly a first object of the present invention to provide a selective reduction type, high temperature superconductor that permits doping with positive holes by selectively reducing constituent elements (atoms).
Another object of the present invention is to provide a method of making a selective reduction type, high temperature superconductor.
In order to achieve the first object mentioned above, there is provided in accordance with the present invention, a selective reduction, high temperature superconductor, wherein it has a portion of its constituent elements selectively reduced whereby it has a superconducting layer thereof doped with positive holes.
The present invention also provides a selective reduction type, high temperature superconductor that has a portion of its constituent elements selectively reduced whereby there are formed in superconducting layers a first and a second region doped overly and doped optimally with superconducting carriers, respectively.
The present invention further provides a selective reduction type, high temperature superconductor that has a portion of its constituent elements selectively reduced whereby the superconductor as a whole has a superconducting carrier concentration such that it is held doped overly or doped optimally with superconducting carriers.
The present invention also provides a selective reduction type, high temperature superconductor that has on each of an upper and a lower surface of a unit lattice thereof a charge supply layer having each of a portion of Cu atoms substituted with a selectively reducible atom.
The present invention also provides a selective reduction type, high temperature superconductor in which the said superconducting layers have an upper and a lower surface constituted by a CuO2 layer of 5-coordination and a layer other than the upper and lower constituted by a CuO2 layer of 4-coordination, the said CuO2 layer of 5-coordination and 4-coordination having been over- and optimum-doped, respectively, by selective reduction.
Further, the present invention provides a selective reduction type, high temperature superconductor having a selectively over-doped and/or a selectively optimum-doped construction.
The present invention further provides a selective reduction type, high temperature superconductor, characterized in that it is made of a (Cu, M) group, high temperature superconducting material, which can be described by composition formula:
Cu1xe2x88x92xMx(Ba1xe2x88x92y,Sry)2(Ca1xe2x88x92zLz)nxe2x88x921CunO2n+4xe2x88x92w
where M represents ions of one or more polyvalent metallic elements selected from the class which consists of Tl, Bi, Pb, In, Ga, Sn, Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, W, Re and Os; L represents one or more elements selected from the class which consists of Mg and alkaline metallic elements; 0xe2x89xa6xxe2x89xa61.0; 0xe2x89xa6yxe2x89xa61; 0xe2x89xa6zxe2x89xa61; 0xe2x89xa6wxe2x89xa64; and 1xe2x89xa6nxe2x89xa616.
The present invention also provides selective reduction type, high temperature superconductor, characterized in that it is made of a (Cu, Tl) group, high temperature superconducting material that can be described by composition formula:
Cu1xe2x88x92xTlx(Ba1xe2x88x92ySry)2(Ca1xe2x88x92zLz)nxe2x88x921CunO2n+4xe2x88x92w
where L represents one or more elements selected from the class which consists of Mg and alkaline metallic elements; 0xe2x89xa6xxe2x89xa61.0; 0xe2x89xa6yxe2x89xa61; 0xe2x89xa6zxe2x89xa61; 0xe2x89xa6wxe2x89xa64; and 1xe2x89xa6nxe2x89xa616.
The present invention also provides a selective reduction type, high temperature superconductor, characterized in that it is made of a (Cu, Tl) group, high temperature superconducting material that can be described by composition formula:
Cu1xe2x88x92xTlx(Ba1xe2x88x92ySry)2(Ca1xe2x88x92zLz)2Cu3O10xe2x88x92w
where L represents one or more elements selected from the class which consists of Mg and alkaline metallic elements; 0xe2x89xa6xxe2x89xa61.0; 0xe2x89xa6yxe2x89xa61; 0xe2x89xa6zxe2x89xa61; and 0xe2x89xa6wxe2x89xa64.
The present invention also provides a selective reduction type, high temperature superconductor, characterized in that it is made of a high temperature superconducting material that can be described by composition formula:
Cu1xe2x88x92xTlx(Ba1xe2x88x92ySry)2(Ca1xe2x88x92zLz)3Cu4O12xe2x88x92w
where L represents one or more elements selected from the class which consists of Mg and alkaline metallic elements; 0xe2x89xa6xxe2x89xa61.0; 0xe2x89xa6yxe2x89xa61; 0xe2x89xa6zxe2x89xa61; and 0xe2x89xa6wxe2x89xa64.
The present invention further provides a selective reduction type, high temperature superconductor, characterized in that selective over- or optimum-doping is effected by decrease in the valence number of ions of a constituent element by decrease in the oxygen concentration, that is by selective reduction, or by varying (increasing or decreasing) oxygen concentration.
The present invention also provides a selective reduction type, high temperature superconductor, characterized in that it is a selectively over-doped type or a selectively optimum-doped type, high temperature superconductor in which n is any one of 3, 4, 5, 6 and 7.
The present invention further provides a selective reduction type, high temperature superconductor having a construction that the reduction of selectively reducible ions causes the ions in the charge supply layers to receive electrons in their outer shell orbits, thereby providing holes in the CuO2 layer of 5-coordination of a said superconducting layer.
The present invention further provides a selective reduction type, high temperature superconductor having a construction that it has a superconducting anisotropy of not greater than 10 and a coherence distance of not less than 3 angstroms.
The present invention further provides a selective reduction type, high temperature superconductor having a construction that said selective reduction transforms its natural superconducting wave function that is of a d-wave high in spatial anisotropy to a wave function of a (d+is) wave that has also a property of an s-wave lacking of spatial anisotropy.
A selective reduction type, high temperature superconductor so constructed as mentioned above according to the present invention can be prepared in a reducing atmosphere or can in use have its oxygen content decreased, yet still maintain a high critical temperature Tc, while providing a reduced aniso-superconductivity xcex3, a high critical current density Jc and a high critical magnetic field Hirr.
Stated otherwise, a selective reduction type, high temperature superconductor according to the present invention is provided with a crystalline and an electronic structure that permits achieving improved Jc and Hirr while maintaining Tc high. Moreover, provided with a superconducting wave function of a (d+is) wave, it is low in superconducting anisotropy. With these advantages, it can be used as a high performance, high temperature superconductor in a variety of industrial sub-fields concerned.
In order to achieve the second object mentioned above, the present invention provides a method of making a selective reduction type, high temperature superconductor, which comprises the steps of: preparing a high temperature superconductor, and heat-treating the prepared high temperature superconductor in a reducing atmosphere.
The present invention also provides a method of making a selective reduction type, high temperature superconductor, comprising the steps of: using an amorphous film as a precursor of high temperature superconductor; causing the amorphous film to grow epitaxially by amorphous phase epitaxy; and heat-treating in a low oxygen, reducing atmosphere the amorphous film that has grown epitaxially.
The present invention further provides a method of making a selective reduction type, high temperature superconductor, comprising the steps of: causing added constituent elements to develop their self-assembling (or self-forming) effect; and causing the high temperature superconductor to grow epitaxially by the self-assembling effect.
A method of making a selective reduction type, high temperature superconductor of the present invention as mentioned above is applicable to making a (Cu, M) group, selective reduction type, high temperature superconductor expressed by composition formula:
Cu1xe2x88x92xMx(Ba1xe2x88x92y,Sry)2(Ca1xe2x88x92zLz)nxe2x88x921CunO2n+4xe2x88x92w
where M represents ions of one or more polyvalent metallic elements selected from the class which consists of Tl, Bi, Pb, In, Ga, Sn, Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, W, Re and Os; L represents one or more elements selected from the class which consists of Mg and alkaline metallic elements; 0xe2x89xa6xxe2x89xa61.0; 0xe2x89xa6yxe2x89xa61; 0xe2x89xa6zxe2x89xa61; 0xe2x89xa6wxe2x89xa64; and 1xe2x89xa6nxe2x89xa616.
A method of making a selective reduction type, high temperature superconductor of the present invention as mentioned above is also applicable to making a (Cu, Tl) group, selective reduction type, high temperature superconductor expressed by composition formula:
Cu1xe2x88x92xTlx(Ba1xe2x88x92ySry)2(Ca1xe2x88x92zLz)nxe2x88x921CunO2n+4xe2x88x92w
where L represents one or more elements selected from the class which consists of Mg and alkaline metallic elements; 0xe2x89xa6xxe2x89xa61.0; 0xe2x89xa6yxe2x89xa61; 0xe2x89xa6zxe2x89xa61; 0xe2x89xa6wxe2x89xa64; and 1xe2x89xa6nxe2x89xa616.
A method of making a selective reduction type, high temperature superconductor of the present invention as mentioned above is also applicable to making a (Cu, Tl) group, selective reduction type, high temperature superconductor expressed by composition formula:
Cu1xe2x88x92xTlx(Ba1xe2x88x92ySry)2(Ca1xe2x88x92zLz)2Cu3O10xe2x88x92w
where L represents one or more elements selected from the class which consists of Mg and alkaline metallic elements; 0xe2x89xa6xxe2x89xa61.0; 0xe2x89xa6yxe2x89xa61; 0xe2x89xa6zxe2x89xa61; and 0xe2x89xa6wxe2x89xa64.
A method of making a selective reduction type, high temperature superconductor of the present invention as mentioned above is also applicable to making a selective reduction type, high temperature superconductor expressed by composition formula:
Cu1xe2x88x92xTlx(Ba1xe2x88x92ySry)2(Ca1xe2x88x92zLz)3Cu4O12xe2x88x92w
where L represents one or more elements selected from the class which consists of Mg and alkaline metallic elements; 0xe2x89xa6xxe2x89xa61.0; 0xe2x89xa6yxe2x89xa61; 0xe2x89xa6zxe2x89xa61; and 0xe2x89xa6wxe2x89xa64.
A method of making a selective reduction type, high temperature superconductor of the present invention so constructed as mentioned above permits manufacturing a positive hole dopable or doped selective reduction type, high temperature superconductor.